Metrology with Synchrotron Radiation

Abstract

Metrology with synchrotron radiation covers a wide range of tasks from radiometry to quantitative materials research. This article provides an overview of activities, methods and facilities in this field. In particular, the measurement capabilities of the Physikalisch-Technische Bundesanstalt (PTB) are presented with the storage rings BESSY II and MLS as primary source standards and cryogenic radiometers as primary detector standards. The applications relate to the characterization of space instruments and optics for EUV lithography, FEL photon diagnostics, nanometrology and material characterizations for semiconductor electronics, photovoltaics, energy storage, catalysis or biotechnology.

Appendix: PTB’s Laboratories at BESSY II and the MLS

PTB’s laboratories and beamlines used for metrology with SR at the MLS and at BESSY II are presented in Figs. A.1 and A.2 and Table A.1, including the so-called BAMline of the BAM Federal Institute for Materials Research and Testing (B5) (Görner et al. 2001). The calculability of SR requires the precise determination of the storage ring parameters and is used within the scope of source-based radiometry at the white-light beamlines M2a and B3a, as well as at the BAMline B5 for the calibration of energy-dispersive detection systems. At BESSY II, they mainly include energy-dispersive X-ray detectors, e.g. for use in reference-free X-ray spectrometry. At the MLS, e.g. spectrometers and energy-dispersive telescope systems for the extra-terrestrial solar observation are characterized in the spectral range of UV, VUV and EUV radiation. Also at the respective neighbouring measuring set-ups M2b and B3b, this refers to spectrometers for UV, VUV and EUV radiation whose calibration will be transferred to secondary radiation source standards, e.g. within the scope of services. The general calibration of radiation detectors, however, is carried out via detector-based radiometry, with cryogenic radiometers as primary standards. By means of the cryogenic radiometers, the radiant power of monochromatized SR can be measured very precisely. Thereby, the entire spectral range – from the UV up to hard X-rays – can be continuously covered at the monochromator beamlines M3 (EUV reflectometry, EUVR) and M4 (Normal Incidence Monochromator, NIM) as well as B1, B2a (Four-Crystal Monochromator, FCM) and B5. Optimized for high stability and spectral purity, also reflectometry with very low uncertainties is carried out at the same beamlines as well as at the beamlines B2b and B6 (X-ray Pencil Beam Facilities, XPBF 1.0 and 2.0) – a relative measurement method which does not require a primary standard.

Fig. 23

Beamlines and instrumentation at the Metrology Light Source (MLS) (PTB 2014)

Fig. 24

Beamlines and instrumentation in the PTB laboratory at BESSY II (PTB 2014)

Table 2 Beamlines used by PTB at the Metrology Light Source and at BESSY II

Source- and detector-based radiometry and reflectometry are used – within the scope of services – to calibrate radiation sources and photodetectors and to characterize optical components. However, the measurement capabilities are extensively to work on – partly – very complex measurement tasks within the scope of cooperation projects with external partners from research and industry. Besides the characterization of space instruments or contributions to photon diagnostics of X-ray laser radiation, the extensive work on the characterization of optical systems for EUV lithography (EUVL), which is carried out at the beamlines M3 and B1 especially in cooperation with the Carl Zeiss SMT GmbH and ASML, is of special importance here. By using scattering methods, also the structures and roughnesses of multilayer mirrors as well as nanostructures, e.g. at EUV lithography masks, can be investigated. Irradiation and lifetime tests on EUVL optics are performed at the dedicated beamlines B3c and B4c. In the X-ray range, measurements and experiments on dimensional nanometrology are performed at the beamline B2a where the methods of X-ray reflectometry and small-angle X-ray scattering are applied to nanostructured surfaces and nanoparticles. A large part of this work takes place within the scope of the European Metrology Programme for Innovation and Research EMPIR as well as the work on X-ray spectrometry which, in turn, concentrates on the beamlines B4b (Plane-reflection Grating Monochromator, PGM), B2a and B5 and on the detection of X-ray fluorescence for material analysis. As radiometrically calibrated instrumentation is used for this purpose, the reference materials can be dispensed with to a large extent, which is of particular importance for the quantification of complex sample systems, e.g. in the fields of microelectronics, photovoltaics or battery research.

Approaches made to quantify material properties on a metrological basis are also pursued at the MLS in cooperation with external working groups, especially of the Berlin universities. At the beamline M1c (Insertion Device Beamline, IDB), the focus is mainly on UV/VUV ellipsometry and electron spectroscopy at surfaces and thin layers, and at the IR beamline M6, on micro spectrometry and on scattered-light scanning near-field optical microscopy (s-SNOM). MLS has been optimized as the worldwide first storage ring for the generation of particularly intensive coherent synchrotron radiation in the THz range and offers very good possibilities at the dedicated THz beamline M5 for the utilization of radiation in this spectral range.